The present invention relates to an electrophotographic copying machine and, more particularly, to sensitivity compensation of a photoreceptor for an electrophotographic copying machine.
An electrophotographic copying machine produces an electrostatic latent image onto a photoreceptor corresponding to an image on a document such as a manuscript or book to be copied. Toner particles are electrostatically adhered to the latent image so that the latent image becomes visible as a toner image. The toner image on the photoreceptor is transferred onto a copy paper via a transference charger. The remaining toner particles and charges on the photoreceptor after transfer to the copy paper are removed for the next copying operation.
Conventionally, the sensitivity of the photoreceptor may inevitably be changed while a plurality of copies are formed. The sensitivity increases after the first several copies have been formed. The sensitivity is not changed as much while a plurality of copies are continuously formed. If the copying operation is stopped for a while, for example, several minutes or more, the sensitivity gradually worsens.
To stabilize the sensitivity of the photoreceptor, the photoreceptor is usually rotated without forming any latent image thereon prior to the start of the copying operation while the other steps are subjected to the photoreceptor in the same manner as when forming the latent image. After these precopy operations are carried out, the copying operation is performed. This complete pre-copy operation takes a long time to perform whereby it takes a long time when copying even a single copy.
The pre-copy operations can be eliminated. For example, the charge voltage on the photoreceptor by the discharger may be detected so that the voltage to be applied to the discharger can be changed. Otherwise, a light source for emitting scanning light toward the document to form the latent image on the photoreceptor can be changed. However, these need the complexity of the conventionally required system which is costly.